Method of compacting material

ABSTRACT

A method of compacting material such as but not limited to cathode material for electrochemical cells. A mixture is inserted into a die cavity and the mixture is compacted into a disk shape by the action of a first plunger pressing down on the material and a second plunger pressing upwardly on the material. Flashing of material during ejection of the disk from the die is prevented by fitting a polymeric sleeve around the outer surface of the first plunger. The sleeve flexes to bulge outwardly and does not enter the die cavity during compaction of material and returns to its original position during ejection of the compacted disk from the die. Contact between the disk and sleeve prevents flashing during ejection. Alternatively, a polymeric seal ring is placed around the outer surface of the first plunger. The disk presses against the seal ring preventing flashing of material during ejection.

FIELD OF THE INVENTION

This invention relates to a method of forming compacted disks, as bycompacting cathode material into disk shape. The invention relates to animproved method of compacting material into disk shape.

BACKGROUND OF THE INVENTION

Primary alkaline electrochemical cells typically have an anodecomprising zinc active material, an alkaline electrolyte, a cathodecomprising manganese dioxide active material, and an electrolytepermeable separator film, typically of cellulose or cellulosic andpolyvinylalcohol fibers, between anode and cathode. Such cell may bedesignated a Zn/MnO₂ cell. The cathode may also contain nickeloxyhydroxide (NiOOH) active material in place of manganese dioxide or inadmixture with manganese dioxide. Such cell containing predominantlynickel oxyhydroxide as the cathode active material, may be designated aZn/NiOOH cell. The alkaline cell casing typically has a cylindricalshape, for example, commonly available in standard cell sizes AAAA (42×8mm), AAA (44×9 mm), AA (49×12 mm), C (49×25 mm) and D (58×32 mm) size.

In the Zn/MnO₂ cell the cathode typically comprises a mixture ofmanganese dioxide, graphite, alkaline electrolyte normally aqueouspotassium hydroxide, and optionally a small amount of binder material,such as polyethylene binder. The manganese dioxide used in the cathodeis preferably electrolytic manganese dioxide (EMD) which is made bydirect electrolysis of a bath of manganese sulfate and sulfuric acid.The EMD is desirable since it has a high density and high purity. Theelectrical conductivity of EMD is fairly low. An electrically conductivematerial is added to the cathode mixture to improve the electricconductivity between individual manganese dioxide particles. Suchelectrically conductive additive also improves electric conductivitybetween the manganese dioxide particles and the cell housing, which alsoserves as cathode current collector. Suitable electrically conductiveadditives can include, for example, conductive carbon powders, such ascarbon blacks, including acetylene blacks, flaky crystalline naturalgraphite, flaky crystalline synthetic graphite, including expanded orexfoliated graphite. The resistivity of graphites such as flaky naturalor expanded graphites can typically be between about 3×10⁻³ ohm-cm and4×10⁻³ ohm-cm.

Alkaline cell cathode for cylindrical shaped cells are normally formedin the shape of disks having a hollow central core. (The term cathodedisks as used herein may also be referenced as cathode pellets ortablets.) The top and bottom surfaces of the disk are flat withcylindrical surface therebetween. A plurality of the disks are typicallyinserted into the cell casing and stacked one on top of the other, forexample, as shown in representative U.S. Pat. No. 6,251,539 B1 forZn/MnO₂ cells and in U.S. Pat. No. 7,273,680 B2 for Zn/NiOOH cells. Thehollow central core of the disks, are bounded by the cathode disk insidesurface running along the disk's central longitudinal axis. The cathodedisk's inside surface is typically of cylindrical shape, but may also beother curvilinear shape either regular or irregular, for example, asshown in U.S. Pat. No. 6,514,637 B2. After the cathode disks areinserted into the cell casing a separator sheet is inserted to line theinside surface of cathode disks, that is, to line the disks' hollowcore. Zinc anode material is then supplied, typically in the form of agelled zinc slurry, to fill the hollow core of the cathode. For example,the zinc particles can be admixed with conventional gelling agents, suchas sodium carboxymethyl cellulose or the sodium salt of an acrylic acidcopolymer, and alkaline electrolyte, normally aqueous potassiumhydroxide. The gelling agent serves to suspend the zinc particles and tomaintain them in contact with one another. Thus, the filled cell hascathode in electrical contact with the casing housing. An elongatedcurrent collector is normally inserted into the anode material. Theelongated current collector is in electrical contact with and end capassembly (insulated from the cell casing). The end cap assembly iscrimped over the cell casing to close the cell as shown, for example, inthe above cited references U.S. Pat. No. 6,251,539 and U.S. Pat. No.7,273,680.

The cathode disks are made by inserting the cathode mixture into a diecavity and activating a punch assembly to compress the cathode mixturewhile in the die cavity. The cathode mixture may be compacted between anupper punch (first punch) and a lower punch (second punch) which form apart of the punch assembly. In the compaction process the upper punchpresses down onto the surface of the cathode mixture while the lowerpunch moves upwards or remains stationary. The compacted cathode disksare ejected from the die by action of a lower plunger which pressesupwards onto the disk's bottom surface, thereby lifting the disk out ofthe die.

A longstanding problem associated with forming such cathode disks foralkaline cells is that as the disk is being ejected from the die,flashing of cathode material tends to form in the small clearance spacebetween the cathode disk and die cavity wall and upper punch. Inparticular flashing of cathode material can become more pronounced whenthe upper punch tip's edge wears. As the upper punch tip edge wears theclearance between the punch and the die cavity wall increases. Suchincrease in clearance creates a void space between disk and die cavitywall which can result in flashing of cathode material as the compactedcathode is being ejected from the die. Such flashing of cathode materialcauses a thin web or wing of cathode material to attach to and protrudefrom the disk's top surface and top edge of the disk's outer surface.Such web of material is shown as flashed material 55 and 55 a protrudingfrom the top of formed cathode disk 50 in FIG. 10. This results in anuneven or nonuniform top edge of the cathode disk and therefore must beremoved before the disk is inserted into the cell.

Moreover, such flashed material breaks off in parts as the cathode diskis being ejected from the die and conveyed and transported to receivingcontainers. This causes an atmosphere of cathode dust to accumulate inthe vicinity of the compaction process. As a safety protection workersmay need to wear protected respiratory masks. The dust contains abrasivecathode material which may gradually collect on the surfaces of thepunch assembly and peripheral operating equipment causing equipmentcontamination.

Accordingly, it is desired to improve the method of forming cathodedisks for alkaline cells in order to eliminate or else significantlyreduce the amount of flashed material which becomes attached to thecathode disk during the disk's formation and compaction.

It is desired to reduce the amount of cathode dust in the atmospheresurrounding the cathode compaction process and compaction of othermaterials thereby improving air quality in the work environment.

SUMMARY OF THE INVENTION

The invention is directed to a method of forming and compacting cathodemixture into cathode disks for insertion into cylindrical casing ofalkaline cells. (Cathode disks are also referenced in the art as cathodepellets or tablets.) Cathode mixtures comprising manganese dioxide,graphite, alkaline electrolyte normally aqueous potassium hydroxide, andoptionally a small amount of binder material, such as polyethylenebinder are formed. The cathode mixture may also contain nickeloxyhydroxide (NiOOH) active material in place of manganese dioxide or inmixture with manganese dioxide. The cathode mixture is inserted into anelongated cavity (die cavity) running through a die. (The term “die” asused herein is equivalent to a housing having a cavity therein). The dieis preferably of ceramic material. A punch assembly is employed tocompress the cathode mixture into a disk shape while the cathode mixtureis in the die cavity. The punch assembly comprises an upper punch (firstpunch), a lower punch (second punch) and a core rod, all of which may beindependently moved in desired synchronized step. The upper punch, lowerpunch and core rod are elongated, typically cylindrically shaped memberscomposed of steel, preferably of high carbon tool steel. The upperpunch, lower punch, and die cavity typically have common centrallongitudinal axis. The upper punch and lower punch typically have ahollow core into which the core rod may penetrate in order to form ahollow central core of the cathode disk as it is being compacted. Thecathode mixture is compacted between upper and lower punch tip surfaces

The cathode mixture is inserted into the die cavity so that it isbetween the tip surface of the upper punch and lower punch. In thecompaction process the upper punch tip surface enters the die cavity andpresses down onto the surface of the cathode mixture while the lowerpunch moves upwards within the die cavity or remains stationary. Acompacted cathode disk is formed as the cathode material is compressedbetween the upper punch tip surface and the lower punch tip surface. Thecompacted cathode material is formed around a core rod resulting in acompacted cathode disk having a hollow central core as in a disk shapeddonut. The top and bottom surfaces of the compacted cathode disk areflat and uniform with a hollow core surrounding the disk's centrallongitudinal axis. The compacted cathode disks are ejected from the diecavity by action of a lower plunger which presses upwards onto thedisk's bottom surface, thereby lifting the disk out of the die while theupper punch lifts away from the die. The cathode disks may be shapedinto required size for insertion in standard cylindrical casing foralkaline cells, for example, AAAA (42×8 mm), AAA (44×9 mm), AA (49×12mm), C (49×25 mm) and D (58×32 mm) size cells. The cathode disks aretypically inserted into the cell casing by stacking a plurality of suchdisks one onto the other. Such alkaline cells typically have an anodematerial comprising a zinc slurry which is inserted into the centralcore of the cathode disks with separator sheet placed in positionbetween the anode and cathode material.

In the method of the invention the cathode disks are formed andcompacted in the die in a manner which eliminates or greatly reduces thechance of forming flashed cathode material. Such flashed material canform a web of cathode material which can attach to the top surface ortop edge of the compacted disks as they are being ejected from the die.As described in the preceding background the formation of such flashedmaterial has been a long standing problem associated with the compactionof cathode disks. The formation of such flashed material is undesirable,since it becomes attached to the cathode disk and easily breaks off inparts as the cathode disk is ejected from the die and conveyed andtransported to receiving containers. This causes an atmosphere ofcathode dust to accumulate in the vicinity of the compaction processrequiring workers to wear protected respiratory masks, and such dust caneventually clog the punch assembly resulting in the need for morefrequent maintenance.

In one aspect the method of the invention has solved this long standingproblem by providing the upper punch (first punch) with a resilient,flexible sleeve, termed herein as a deflasher sleeve. The deflashersleeve is slipped over and around the lower body surface of the upperpunch adjacent the punch tip surface. The deflasher sleeve is desirablyof a resilient, durable elastomeric material or a thermoplastic materialwhich also exhibit some elastomeric properties. A preferred material forthe deflasher sleeve is polyurethane. In its original or startingposition, the deflasher sleeve fits circumferentially flush against theupper punch surface thereby contacting and hugging the upper punch outersurface. However, the sleeve has the ability to compress causing a majorportion of the sleeve (middle portion) to flex and bulge outward fromthe upper punch outer surface as the sleeve presses against the dietable (die top surface). This occurs just as the upper punch penetratesinto the die cavity and just before the upper punch tip surface pressesonto the cathode mixture. No portion of the deflasher sleeve enters thedie cavity as the upper punch presses onto the cathode mixture or at anyother time during the process. Instead the deflasher sleeve contacts thedie only at the die table (die top surface) without entering the diecavity. After the cathode disk has been compacted within the die cavitythe upper die lifts upwards causing the deflasher sleeve to reflex toits original position lying flush against and hugging the outer surfaceof the upper punch. As the lower punch moves upwards to eject thecompacted cathode disk from the die cavity the top surface or top outeredge of the compacted disk impinges against the deflasher sleeve just asthe sleeve has reflexed back to its original position. The impingementof the cathode disk against the resilient deflasher sleeve prevents theformation of flashed material from forming and attaching to the uppersurface of the compacted disk as the disk is being ejected from the die.Although the deflasher sleeve formed of polyurethane material appears towork best in preventing deflashing of cathode material, it will beappreciated that other material having similar resiliency, durability,and particle abrasion resistant properties may also be suitable in placeof polyurethane. Thus, the invention is not intended to be limited touse of polyurethane material for the deflasher sleeve.

In another aspect of the invention the lower end of the upper punch(first punch) outer surface may be over molded with a seal ring composedof resilient, durable polymer, preferably polyurethane. The seal ringthus lies circumferentially flush around the outer surface of the upperpunch at the lower end of the upper punch. The resilient polymer,preferably polyurethane, is molded circumferentially over a portion ofthe upper punch outer surface adjacent to but not contacting the punchtip surface. Thus, a ring of molded polymer, preferably of polyurethane,is formed around the lower end of the upper punch forming thereby a sealring. Preferably, a plurality of apertures, typically round apertures,are formed along a circumferential path in the upper punch outer surfacebefore the seal ring of polyurethane or equivalent polymer is moldedonto the upper punch surface. In this case the apertures will underliethe polyurethane ring as this polymer is molded over the upper punchbody surface. Such apertures underlying the seal ring serve to hold oranchor the molded polymer ring to the upper punch surface. The aperturesalso provide compression space into which the overlying portions of theseal ring may be compressed as contact pressure is applied to the sealring.

In application of the seal ring in the compaction method of theinvention, the cathode mixture is first inserted into the die cavity sothat it rests on the tip surface of the lower punch (second punch). Thelower punch may be held stationary (or else move upwards) as the upperpunch (first punch) moves downwards into the die cavity to compact thecathode mixture. As the upper punch moves downwards into the die cavityto compact the cathode disk against the lower punch tip surface, atleast a portion of the seal ring squeezes into the die cavity entrance.After the cathode mixture is compacted into a disk shape, the lowerpunch pushes upwards to eject the compacted cathode from the die.However, the seal ring provides a tight seal at the entrance of the diecavity immediately above the cathode disk while the disk is still in thedie cavity. The cathode disk presses against the seal ring just as thedisk is being ejected from the die, but while at least a portion of theseal ring is still within the die cavity. The pressing action betweenthe cathode disk and seal ring while at least a portion of the seal ringis still in the die cavity, prevents cathode material from flashing andattaching to the disk surface as the disk is being ejected from the die.Polyurethane is a preferred material for the seal ring but otherelastomeric polymer having similar property of resiliency, durability,and particle abrasion resistance may also be suitable. For example, anydurable elastomeric material such as vulcanized rubber, styrenebutadiene (SBR) rubber, or silicone rubber and similar materials may besuitable substitute material for polyurethane for the seal ringcomposition. Thus, the invention is not intended to be limited to use ofpolyurethane material for the seal ring.

The compacted disk shape is typically cylindrical (coin shape), havingopposing parallel flat top and bottom surfaces with integral cylindricalbody surface therebetween. However, the method of the invention is notintended to be limited to forming such regular shaped disks. Thecompacted disk may be of other shape or configuration. For example, thecompacted disk formed by the method of the invention may have regular orirregular shaped circumferential edges. Thus, the disk's circumferentialedge may be formed of straight or curvilinear surfaces or a portion ofthe circumferential edge may be straight and another portion may becurvilinear.

The method of the invention and improvements herein described can beapplied to compaction of other materials. The invention is therefore notintended to be limited to compaction of cathode material for batteries.The application of the method of the invention and improvements hereindescribed can be applied to other compaction processes. For example, theinvention can be applied to compacting pharmaceutical powders or othertypes of cakes or pellets which may be compacted. The constituents forsuch cakes or powders may be of differing chemical composition. Theinvention and improvements herein described can be beneficially appliedto compacting various materials, for example, but not limited to,compacting pharmaceutical powders or other materials wherein powder orparticulate matter or chemical compositions must be compacted intovarying shapes or configurations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of the of a first embodiment of thepunch assembly showing the deflasher sleeve in compressed, flexedposition as the cathode material is being compacted into a disk.

FIG. 2 is a cross sectional view of the punch assembly showing thedeflasher sleeve in reflexed position lying flush against the outersurface of the upper punch as the compacted cathode disk is beingejected from the die.

FIG. 3 is a pictorial view of the deflasher sleeve in flexed positionaround the upper punch.

FIG. 4 is a pictorial view of the deflasher sleeve in original orreflexed position lying flush against the outer surface of the upperpunch.

FIG. 5 is an exploded view of the upper punch and deflasher sleeve.

FIG. 6 is a pictorial view of the deflasher sleeve inserted over thelower body surface of the upper punch.

FIG. 7 is a cross sectional view of a second embodiment of the punchassembly showing a seal ring over the bottom end of the upper punchouter surface and adjacent the punch tip surface.

FIG. 8 is a pictorial view of the upper punch showing a plurality ofapertures in the upper punch body surface adjacent the punch tipsurface.

FIG. 9 is a pictorial of the upper punch showing a seal ring coveringthe underlying apertures shown in FIG. 8.

FIG. 10 is a schematic pictorial representation showing flashed cathodematerial attached to the upper surface of the compacted cathode diskwhich may occur when the deflasher sleeve as in FIG. 1 or the seal ringas in FIG. 7 are not employed.

FIG. 11 is a schematic pictorial representation showing a compactedcathode disk without flashed cathode material attached thereto as aresult of employing either the deflasher sleeve as in FIG. 1 or the sealring as in FIG. 7.

DETAILED DESCRIPTION

A representative cathode mixture 50 for an alkaline cell is prepared.The cathode mixture 50 is intended to be compacted into cathode disks,typically cylindrical shaped disks having a hollow core, for insertioninto a cell casing. The compacted cathode disks may be inserted, forexample, in a conventional cylindrical alkaline cell having an anodecomprising zinc, as referenced hereinabove and in representative U.S.Pat. No. 6,251,539 B1. The intended use of the compacted cathode disksmay be, for insertion in standard size cylindrical casing for alkalinecells, for example, AAAA (42×8 mm), AAA (44×9 mm), AA (49×12 mm), C(49×25 mm) and D (58×32 mm) size cells.

A representative cathode mixture 50 comprises manganese dioxide (EMD)and a conductive carbon, preferably, graphitic material, desirably aflaky crystalline natural graphite or expanded graphite or mixturethereof. Cathode mixture may also include graphitic carbon fibers orgraphitic carbon nanofiber. The total conductive carbon in the cathodemixture desirably comprises between about 2 and 10 percent by weight ofthe cathode, preferably between about 2 and 8 percent by weight of thecathode. The cathode mixture also desirably comprises between about 5and 10 percent by weight of an aqueous solution of KOH, which preferablyhas a strength of between about 7 and 10 Normal (30 and 40 wt. % KOH and2 wt. % ZnO).

The cathode active material, typically comprising manganese dioxide(EMD), comprises between about 80 and 92 percent by weight of thecathode mixture, preferably between about 80 and 90 percent by weight ofthe cathode mixture. The cathode disk 50 (FIG. 11) formed by the methodof the invention can desirably have the following composition: 87-93 wt% of electrolytic manganese dioxide (e.g., Trona D from Kerr-McGee), 2-6wt % (total) of graphite, 5-7 wt % of a 7-10 Normal aqueous KOH solutionhaving a KOH concentration of about 30-40 wt %; and 0.1 to 0.5 wt % ofan optional polyethylene binder. The electrolytic manganese dioxidetypically has an average particle size between about 1 and 100 micron,desirably between about 20 and 60 micron. The graphite is typically inthe form of natural, or expanded graphite or mixtures thereof. Thegraphite can also comprise graphitic carbon nanofibers alone or inadmixture with natural or expanded graphite. Such cathode mixtures areintended to be illustrative and are not intended to restrict thisinvention.

The term “graphite” or “graphitic material” as used herein shall includenatural and synthetic crystalline graphites (synthetically prepared orprocessed graphite), expanded graphites, graphitic carbons, andgraphitic carbon fibers. The natural or expanded graphite is preferablyin particulate form having a mean average particle size desirablybetween about 0.5 micron and 50 micron, typically between about 10micron and 50 micron. A graphitic carbon has the characteristics of anordered three-dimensional graphite crystalline structure consisting oflayers of hexagonally arranged carbon atoms stacked parallel to eachother as determined by X-ray diffraction. As defined in InternationalCommittee for Characterization and Terminology of Carbon (ICCTC, 1982),published in the Journal Carbon, Vol. 20, p. 445, a graphitic carbonembraces the varieties of substances consisting of elemental carbon inallotropic form of graphite irrespective of structural defects. The termgraphitic carbon as used herein shall be construed in this manner.

In one specific embodiment the representative cathode mixture 50 may beinserted into die assembly 10 (FIG. 1) to be compacted into a cathodedisk 50 (FIG. 11). Compacted disk 50 has an outer surface 54 and aninner surface 52 defining a central hollow core 51 (FIG. 11). The dieassembly 10 (FIGS. 1 and 2) has die 20 with die cavity 25 therein, anelongated upper punch (first punch) 30, an elongated lower punch (secondpunch) 40, and a core rod 60 which moves within the hollow core 45 oflower punch 40. The upper punch 30 is an elongated cylindrical memberhaving a hollow core 35. Similarly lower punch 40 is an elongatedcylindrical member having a hollow core 45 (FIG. 2). Core rod 65 mayalso have a hollow core 65. Lower punch 40 is integrally connected tobase 46 (FIG. 2). The die cavity 25, upper punch 30, lower punch 40, andcore rod 60 all have common central longitudinal axis 28 (FIG. 1). Upperpunch 30 and lower punch 40 moves within die cavity 65. The upper punch30 and lower punch 40 are formed of high carbon steel desirably toolgrade steel. Die 20 is formed preferably of ceramic material. The upperpunch 30 is fitted with a deflasher sleeve 70 of resilient, durable,polymeric material (FIG. 6). Deflasher sleeve 70 desirably haselastomeric properties and may be of thermoplastic material havingelastomeric properties. Preferably sleeve 70 is of polyurethanematerial, but it will be appreciated that other elastomeric materialshaving similar durability and elastomeric properties could be employedin place of the polyurethane. A preferred polyurethane for sleeve 70 isavailable as polyester-85A polyurethane available from Parkway Products.Deflasher sleeve 70 is of a cylindrical shape having a cylindrical outersurface 74 and hollow core 71 defined by inner surface 72 (FIG. 5). Inthe position shown in FIGS. 5 and 6 the deflasher sleeve 70 is in itsoriginal position flush against the outer surface of upper punch 30 sothat it contacts and hugs the outer surface of upper punch 30 as shownin FIGS. 2, 4, and 6. The cathode compaction method of the inventionemploying the die assembly 10 shown in FIGS. 1 and 2 is as follows:

Initially the upper punch 30 (FIG. 1) is moved upwards so that upperpunch tip 32 is above die table (die top surface) 22. The cathodemixture 50 is inserted into die cavity 25 so that the mixture lodgesagainst tip surface 42 of lower punch 40. The cathode mixture 50 is thusinitially held in place in die cavity 25 by lower punch tip surface 42,core rod 60 outer surface 64, and the wall surface of cavity 25. Upperpunch 30, lower punch 40, and core rod 60 have independent movement, andmay be moved up or down in synchronized manner. With reference to thepunch assembly 10 shown in FIGS. 1 and 2 the cathode mixture 50 iscompacted by action of upper punch 30 stroking downward on cathodemixture 50 as lower punch 40 remains stationary or moves upwards insynchronized timing with the downward movement of upper punch 30. Corerod 60 (FIGS. 1 and 2) may slide independently to form and maintain thecathode disk hollow core 51 shown best in FIG. 11.

In a preferred compaction sequence the cathode mixture 50 is firstloaded into die cavity 25 (FIG. 1) while the upper punch tip 32 isextended above die table 22 (loading position not shown). Upper punch 30is then pushed downward while lower punch 40 and core rod 60 is movedupward further into the die cavity to the position shown in FIG. 1. Asthe upper punch 30 is pushed downward, tip surface 32 of upper punch 30moves down passed the die table (top surface) 22 of die 20. This causesa major portion of sleeve 70, namely its middle portion, to compress,that is, to flex and bulge outwardly as the sleeve is held in place atits upper end by upper punch head ring 34 and at its lower end by impactagainst die table 22 (FIGS. 1 and 3). Deflasher sleeve 70 does not enterthe die cavity 25. The pressure of the lower edge of sleeve 70 againstthe die table 22 as upper punch 30 moves down into die 22 causes thebulging of the sleeve to occur (FIG. 3). No portion of sleeve 70 entersdie cavity 25. Compaction of cathode mixture 50 occurs as the upperpunch 30 continues downward movement once the lower punch 40 reaches theposition shown in FIG. 1. (Compaction of cathode mixture 50 may beassisted by simultaneous continued upward movement of lower punch 40 asthe upper punch 30 continues downward.) The cathode mixture 50 thusbecomes compacted between tip surface 32 of upper punch 30 and tipsurface 42 of lower punch 40 while the deflasher sleeve 70 iscompressed, that is, becomes flexed outwardly in bulged position shownin FIGS. 1 and 3. After cathode mixture 50 has been compacted the upperpunch 30 begins to retract. The deflasher sleeve 70 remains flexed andoutwardly bulged as shown in FIG. 1 until the upper punch 30 is fullyretracted, that is, until upper punch tip surface 32 reaches die table22. At that point deflasher sleeve 70 reflexes to return to its originalposition (FIG. 2). However, while the upper punch 30 is retracting, thelower punch 40 is simultaneously moving upward to begin ejection of thecompacted cathode 50 from die cavity 25. The upwards movement of lowerpunch 40 is timed so that the compacted cathode 50 bumps into deflashersleeve 70 just as the deflasher sleeve 70 returns to its originalreflexed, decompressed, position hugging the outer surface of upperpunch 30 (FIG. 2). The point of contact occurs during ejection ofcathode disk 50 just as the cathode disk outer surface 54 contacts thelower portion of sleeve 70 as shown in FIG. 2. The forced contactbetween compacted cathode 50 and deflasher sleeve 70, is timed to occurjust before compacted cathode 50 is fully ejected from die cavity 25.This has been found to prevent formation of flashed cathode materialsuch as the web of flashed material 55 and 55 a attached to the topsurface 53 cathode disk 50 as shown in FIG. 10. Such flashed material 55and 55 a may occur, that is, if sleeve 70 of the invention was notemployed. Thus, the product cathode disk 50 ejected from die 25 does notexhibit flashed material 55 and 55 a attached to its surfaces as in FIG.10, but rather has even (clean) surfaces as shown in disk 50 of FIG. 11.

In another specific embodiment the representative cathode mixture 50 maybe inserted into die assembly 10 (FIG. 7) to be compacted into a cathodedisk 50 (FIG. 11). The die assembly 10 (FIG. 7) has die 20 with diecavity 25 therein and an elongated upper punch 30 and an elongated lowerpunch 40, which move within die cavity 25. There is a core rod 60 whichmoves within the core cavity 45 of lower punch 40. The die cavity 25,upper punch 30, lower punch 40, and core rod 60 all have common centrallongitudinal axis 28 (FIG. 7). The upper punch 30 and lower punch 40 areformed of high carbon steel desirably tool grade steel. Die 20 is formedpreferably of ceramic material. The upper punch 30 is fitted with a sealring 80, preferably of polyurethane material, as shown best in FIG. 9. Apreferred polyurethane for seal ring 80 is available as polyester-85Apolyurethane available from Parkway Products. Preferably the durometerhardness of the polyurethane seal ring 80 ranges from 20 Shore A to 70Shore D (ASTM Standard). The seal ring 80 is preferably overmoldeddirectly onto the upper punch outer surface at the punch lower end 38(FIGS. 8 and 9). Seal ring 80 thus lies circumferentially flush againstthe outer surface of lower punch 40, thereby hugging the outer surfaceof said lower punch 40. The seal ring 80 is thus positioned adjacent andin close proximity to the punch tip surface 32, but does not cover tipsurface 32 (FIG. 9). Preferably, a plurality of apertures 37 (FIG. 8)are formed along a circumferential path in the punch body surface andthe seal ring 80 is molded directly over apertures 37, thus coveringthese apertures. The cathode mixture loading and compacting processemploying the die assembly 10 shown in FIG. 7 is as follows:

Initially the upper punch 30 (FIG. 7) is moved upwards so that upperpunch tip 32 is above die table (die top surface) 22. The cathodemixture 50 is inserted into die cavity 25 so that the mixture restsagainst tip surface 42 of lower punch 40. The cathode mixture 50 is thusinitially held in place in die cavity 25 by lower punch tip surface 42,core rod 60 outer surface 64, and the wall surface of cavity 25. Upperpunch 30, lower punch 40, and core rod 60 have independent movement, andmay be moved up or down in synchronized manner. With reference to thepunch assembly shown in FIG. 7 the cathode mixture is compacted byaction of upper punch 30 stroking downward on cathode mixture 50 aslower punch 40 moves up into desired position as shown best in FIG. 7.Core rod 60 (FIGS. 1 and 2) may slide independently to form the cathodedisk hollow core 51 shown best in FIG. 11.

In a preferred compaction sequence the cathode mixture 50 is firstloaded into die cavity 25 (FIG. 7) while the upper punch tip 32 isextended above die table 22 (loading position not shown). Upper punch 30is then pushed downward while lower punch 40 and core rod 60 is movedupward further into the die cavity to the position shown in FIG. 7. Asthe upper punch 30 is pushed downward, tip surface 32 of upper punch 30moves down passed the die table (top surface) 22 of die 20. This causesat least a portion of the seal ring 80 to compress as seal ring 80begins entry into die cavity 25 (FIG. 7). The seal ring 80, however, ismolded to the outer surface of upper punch 30 at punch lower end 38 andtherefore continues to hug punch 30 outer surface. Compaction of cathodemixture 50 occurs as the upper punch 30 continues downward movement oncethe lower punch 40 reaches the desired position, approximately as shownin FIG. 7. (Compaction of cathode mixture 50 may be assisted bysimultaneous upward movement of lower punch 40 as the upper punch 30continues downward.) During cathode compaction vertical forces on theseal ring 80 are transposed into radial forces enhancing the sealingeffect of seal ring 80 as the sealing ring 80 begins to enter die cavity25 (FIG. 7). This helps to prevent formation of flashed cathode materialat this point in the compaction process. After cathode mixture 50 hasbeen compacted the upper punch 30 begins to retract. (The seal ring 80remains compressed until the upper punch tip surface 32 retracts to dietable 22.) However, while the upper punch 30 is retracting, the lowerpunch 40 is simultaneously moving upward to begin the process ofejecting the compacted cathode 50. During the beginning of the ejectionprocess, the seal ring 80 continues to form a tight plug at the entranceto cavity 25, that is, just at or immediately below die table 22. Thatis, as the cathode disk 50 is being ejected from die cavity 25 cathodedisk 50 presses against seal ring 80, while at least a portion of sealring 80 is still within die cavity 25. This prevents flashing of cathodematerial to occur or become attached to the cathode disk 50 as disk 50is being ejected from die cavity 25. Such flashed material 55 and 55 amay otherwise occur, that is, if seal ring 80 of the invention is notemployed around the lower end 38 of upper punch 30. Thus, the productcathode disk 50 ejected from die 25 does not exhibit flashed material 55and 55 a attached to its surfaces as in FIG. 10, but rather has even(clean) surfaces as shown in disk 50 of FIG. 11.

Although the invention has been described with reference to specificembodiments, it should be appreciated that other embodiments arepossible without departing from the concept of the invention and arethus within the claims and equivalents thereof.

1. A method of forming a compacted disk, comprising the steps of: a)inserting a mixture of material into a cavity running through a diecasing, b) positioning a first plunger in alignment with said cavity sothat said first plunger may engage said mixture of material when saidfirst plunger is moved downwardly into said cavity, c) positioning asecond plunger in alignment with said cavity so that said second plungermay engage said mixture of material when said second plunger is movedupwardly into said cavity, d) positioning a flexible polymeric sleevecircumferentially around at least a portion of the outer surface of saidfirst plunger so that said sleeve lies flush against at least a portionof the outer surface of said plunger, thereby hugging the outer surfaceof said plunger, e) moving said first plunger downwardly into saidcavity so that said mixture of material is compacted against a portionof said second plunger thereby forming a compacted disk, wherein as saidfirst plunger moves downwardly into said cavity to compact said mixtureof material, a major portion of said polymeric sleeve flexes outwardlyto bulge away from the outer surface of said first plunger, f) ejectingsaid compacted disk from said cavity by moving said first and secondplungers upwardly within said cavity, wherein as said first plungermoves upwardly said sleeve reflexes to lie flush against the outersurface of said first plunger thereby hugging the outer surface of saidfirst plunger, wherein said compacted disk contacts at least a portionof said reflexed sleeve as said compacted disk is being ejected fromsaid cavity, and wherein said contact between said compacted disk andsaid reflexed sleeve prevents a web of flashed material from forming andattaching to said compacted disk as the disk is being ejected from thecavity.
 2. The method of claim 1 wherein no portion of said polymericsleeve enters said cavity at any time during steps (a) through (e). 3.The method of claim 1 wherein said polymeric sleeve comprisespolyurethane.
 4. A method of forming a compacted cathode disk for analkaline cell, comprising the steps of: a) inserting a mixture ofcathode material into a cavity running through a die casing, b)positioning a first plunger in alignment with said cavity so that saidfirst plunger may engage said cathode material when said first plungeris moved downwardly into said cavity, c) positioning a second plunger inalignment with said cavity so that said second plunger may engage saidcathode material when said second plunger is moved upwardly into saidcavity, d) positioning a flexible polymeric sleeve circumferentiallyaround at least a portion of the outer surface of said first plunger sothat said sleeve lies flush against at least a portion of the outersurface of said plunger, thereby hugging the outer surface of saidplunger, e) moving said first plunger downwardly into said cavity sothat said cathode material is compacted against a portion of said secondplunger thereby forming a compacted cathode disk, wherein as said firstplunger moves downwardly into said cavity to compact said cathodematerial, a major portion of said polymeric sleeve flexes outwardly tobulge away from the outer surface of said first plunger, f) ejectingsaid compacted cathode disk from said cavity by moving said first andsecond plungers upwardly within said cavity, wherein as said firstplunger moves upwardly said sleeve reflexes to lie flush against theouter surface of said first plunger thereby hugging the outer surface ofsaid first plunger, wherein said compacted cathode disk contacts atleast a portion of said reflexed sleeve as said cathode disk is beingejected from said cavity, and wherein said contact between said cathodedisk and said reflexed sleeve prevents a web of flashed cathode materialfrom forming and attaching to said compacted cathode disk as the disk isbeing ejected from the cavity.
 5. The method of claim 4 wherein saidfirst and second plungers each have a tip surface, wherein each of saidtip surfaces contact said cathode material as said cathode material isbeing compacted in step (e).
 6. The method claim 5 wherein said firstand second plunger tip surfaces each form a flat annular surface.
 7. Themethod of claim 4 wherein a rod passes through the center of saidcathode material as said cathode material is being compacted in step(e).
 8. The method of claim 4 wherein no portion of said sleeve enterssaid cavity at any time during said steps (a) through (f).
 9. The methodof claim 4 wherein said polymeric sleeve comprises polyurethanematerial.
 10. The method of claim 4 wherein said die casing comprisingceramic material.
 11. The method of claim 4 wherein said first andsecond plungers each have a cylindrical outer surface and said first andsecond plungers are each of steel.
 12. The method of claim 7 whereinsaid first and second plungers each have an elongated housing having anelongated hollow core running there through and said rod passes throughsaid hollow core of at least one of said first and second plungers asthe cathode material is being compacted in step (e).
 13. The method ofclaim 4 wherein said cathode material comprises manganese dioxide.